Assessing microbial lipid contributions during laboratory degradations of fats and oils and pure triacylglycerols absorbed in ceramic potsherds

In order to better interpret the origins of degraded fats and plant oils, experiments have been performed in the laboratory to simulate the decay of such commodities during burial. The progress of decay of various acyl lipids (milk and olive oil) and pure compounds (triolein and tristearin) has been monitored for up to 126 days. A general pattern emerged of a rapid decrease in triacylglycerol abundance with a concomitant increase in free fatty acids as a result of ester hydrolysis. The hydrolysis was assumed to be mediated largely by micro-organisms since this loss of triacylglycerol was accompanied by an overall consumption of lipid in all experiments. The appearance of microbial lipids occurred in the latter stages of degradation; these included short and long straight-chain, and branched-chain fatty acids ranging between C14 and C20. Ergosterol, a characteristic fungal marker, was also seen in the degradation experiment involving milk. The extent of incorporation of bacterial and fungal markers in decay experiments was minor (<2%) even in the case of highly degraded lipids (>90% consumed), thus fully legitimising the use of absorbed lipids in archaeological investigations.